The Triodion 

The Triodion (Gk., "book of three odes";  Slav. Póstnaya Triód, "penitential" or "fasting triodion") contains the special prayers and hymns used during the Great Fast.   The title Triodion refers to the small canons with only three odes which are sung at Matins on weekdays of the Fast.   Because the Pentecostarion is sometimes called a Triodion as well (Slav. Tsvetnaya Triód, "flowery" or "festal triodion"), the more specific title Lenten Triodion is often used to distinguish the two books.

Contents of the Triodion

The "time of the Triodion" (another name for the season of the Great Fast) begins with the Sunday of the Publican and the Pharisee.  This Sunday and the next Sunday, the Sunday of the Prodigal Son, have special hymns that prepare us for the Fast

Beginning with the following Saturday, the Triodion has proper hymns for every day through the end of the Great Fast:

The Saturday of the Departed
The Sunday of the Last Judgment (Sunday of Meatfare)
Monday through Friday of Cheesefare Week
Saturday of Cheesefare Week (Memory of the Holy Ascetics)
The Sunday of Forgiveness (Sunday of Cheesefare; the fast begins on Sunday evening)
The First Week of the Great Fast
The First Sunday of the Great Fast
The Second Week of the Great Fast
The Second Sunday of the Great Fast
The Third Week of the Great Fast
The Third Sunday of the Great Fast
The Fourth Week of the Great Fast
        On Thursday, the Great Canon of St. Andrew of Crete is sung
        On Saturday, the Akathist Hymn to the Theotokos is sung
The Fourth Sunday of the Great Fast
The Fifth Week of the Great Fast
The Fifth Sunday of the Great Fast
The Sixth Week of the Great Fast

The Great Fast comes to an end at sundown on Friday of the sixth week.  The next eight days, from Lazarus Saturday to Great and Holy Saturday, make up Great and Holy Week.

In the Russian Orthodox Church before the reforms of the Patriarch Nikon, the Triodion ended with the final Friday of the Great Fast, and the materials for Great and Holy Week, Pascha, and the Paschal Season were found in the Pentecostarion. This division of the Triodion is still used in the pre-Nikonian Russian Old Rite, and was also used in Church Slavonic liturgical books in the Catholic churches of the Ruthenian Rite, who broke with Moscow before the Nikonian reforms. 

On the other hand, the Russian Orthodox churches which follow the New Rite, as well as most other Orthodox Christians, place the Holy Week materials in the Lenten Triodion, and begin the Pentecostarion with the feast of Pascha.  This organization is usually followed in those Byzantine Catholic liturgical books produced in English.

The Triodion in Church Slavonic

A Triodion was published in L'vov around 1900, but no copy was available at this writing so that further information could be provided.  However, the L'vov Pentecostarion produced around the same time followed the Old Rite division described above, so one could safely assume that the L'vov Triodion contained liturgical materials from the Sunday of the Publican and the Pharisee through Friday of the sixth week of the Great Fast.

No new edition of the Triodion was published as part of the Ruthenian reform of the 1940's.

A Triodion in Church Slavonic following the Great Russian usage is available on-line, courtesy of St. Sergius of Radonezh Russian Orthodox Cathedral, Parma, Ohio.

The Triodion in English

In 1969, Mother Mary of the (Orthodox) Monastery of the Veil, and Archimandrite (now Bishop) Kallistos Ware published a Lenten Triodion containing selected material for the Great Fast:

The Pre-Fast Sundays, and the Saturday of the Dead
The First Week of the Great Fast
The Sundays of the Great Fast
The Thursday of the Great Canon
The Saturday of the Akathist
Great and Holy Week

This volume contains excellent explanatory material and rubrics for the services, along with a preface on the meaning of the Great Fast, and the rules for fasting.  In 1979, a companion volume of Supplementary Services was printed by the Monastery of the Veil which provides the days not originally included in Mother Mary's Lenten Triodion.  

In 1995, the Sisters of Saint Basil the Great in Uniontown, Pennsylvania published a complete Lenten Triodion, which has become the standard Triodion used in the Byzantine Catholic Church.  It includes the Office of Matins, and the Hour;  however, a lack of rubrics and explanatory material make it necessary for those new to the Triodion to consult the Typikon, or Mother Mary's book, to understand how the hymns are to be used.

In 2000-2001, a Lenten Triodion according to the Melkite usage (in four volumes) was published by Sophia Press.